The foreign-born population in the United States has more than tripled in the last thirty years. Past research indicates that many immigrants to the United States experience greater risks overtime for substance abuse and psychiatric disorders, and are less likely to seek treatment for these health-related problems. To better understand the impact of immigration on substance abuse, mental health, and treatment gaps among adults, we will investigate: (1) whether and how (a) excessive and problematic alcohol use, (b) illegal drug use, (c) alcohol and drug use disorders, and (d) psychiatric disorders vary by nativity (foreign-born status) and immigrant characteristics (years in the United States and refugee status);(2) whether and how comorbidity between substance use and psychiatric disorders vary by nativity and immigrant characteristics;(3) whether and how (a) seeking treatment for alcohol and drug use problems and (b) seeking treatment for mental health problems vary by nativity and immigrant characteristics;and, (4) whether and how the incidence of acquiring or recovering from (a) excessive and problematic alcohol use, (b) illegal drug use, (c) alcohol and drug disorders, or (d) psychiatric disorders over a three-year period varies by nativity and immigrant characteristics. We consider these relationships separately for six racial-ethnic groups: African, Asian/Pacific Islander, European, Mexican, Puerto Rican, and other Hispanics/Latinos. Our analysis will use the first and second waves of the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC) that include sufficiently detailed data on the health-related outcomes that we are able to measure the timing of the outcomes. The proposed study will provide prevalence and incidence rates that are adjusted for key confounding factors, such as social and economic characteristics, perceived discrimination, traumatic events, and perceived stress. The proposed study will give policy makers information they need to develop more effective and targeted services and intervention programs aimed at bettering the health and well being of immigrants in the United States. Public Health Relevance: The goal of the proposed study is to increase understanding of immigrant differences in excessive alcohol use, illicit drug use, substance use and psychiatric disorders, comorbidity between those disorders, and treatment gaps in addressing these adverse health-related problems. The study will investigate these immigrant differences separately for six racial-ethnic groups (African, Asian/Pacific Islander, European, Mexican, Puerto Rican, and other Hispanics/Latinos) taking into account variation in social support, acculturation, discrimination, and stress.